This invention relates to webs, such as polymeric webs, having a surface with a multiplicity of features used for fastening or joining. Such features may be stems, loops and other surface features that can mechanically interlock with features, such as fibers or protrusions, on an opposing surface.
Hook and loop fasteners, such as those currently marketed under the xe2x80x9cScotchmatexe2x80x9d trademark by Minnesota Mining and Manufacturing Company, St. Paul, Minn. (3M) are a known type of mechanical fastener. One alternative to a hook is a mushroom-shaped protrusion or stem which can also be used as hermaphroditic mechanical fastener by engaging other protrusions or surface features rather than loops.
U.S. Pat. Nos. 4,056,593 and 4,959,265, disclose methods of extruding polymeric webs with upstanding stems. In the hook surface of U.S. Pat. No. 5,077,870, a single component thermoplastic resin is extruded onto a tool which has an array of cavities which, upon separation from the resin, form an array of stems. The stems then are calendered to produce a broader head (cap or mushroom head) at the top of the stem. U.S. Pat. No. 5,393,475 discloses a method of making a stemmed web with stems on both sides using two different materials.
Despite current advances in the art, there is a need for stemmed webs, such as mechanical fasteners, that have a wider variety of properties to meet more varied applications.
For purposes of this description, a stem refers to a promotion from a surface, such as a web, regardless of the shape, length, length-to-width-ratio, or other characteristics of the protrusion provided that the stem can mechanically interlock or engage with a mating surface having other features such as stems, loops or fibers. A stemmed web is a web having on at least one surface small or features such as hooks and stems.
The present invention is a web of material having a plurality of stems extending from at least one side of the web. The web includes at least a first layer of material having a first side and a second side and a second layer of material. The second layer of material has a first side which faces the first side of the first layer and a second side from which the plurality of stems protrude. The first and second layers of material may be, but need not be, joined together while one or both of the layers are molten and before the molten layer or layers have cooled.
The first layer is formed from an elastic material and the second layer of material can be formed of thermoplastic material or melt processable polymeric material. The first layer of material differs from the second layer of material and in one embodiment the material forming the first layer protrudes into and forms at least part of the stems formed on the second layer.
In other alternative embodiments, both surfaces of the web can have stems, and one or more of these stems can have caps. Additional layers of material also can be formed and joined together with the first and second layers.
The invention also includes a method of making a web of material having a plurality of stems. The method includes selecting a first elastic material for a first layer of material and selecting a second material for a second layer of material. The first and second layers of material are melt formed. The first and second layers of material are joined to form a two-layer sheet. Next, a plurality of stems are formed on at least the second layer of material.
The stems can be formed by pressing the multiple layer sheet against at least one temperature controlled surface containing an array of holes to form an array of stems. Caps can subsequently be formed on the tips of the stems by pressing the stems against a heated surface to form caps on the tips of the stems.
Alternatively, the stems can be formed by extruding multiple layers of a thermoplastic or melt processable material through a shaped die to form a multiple layer sheet having a plurality of raised ribs on at least one surface. A plurality of sharp edges is passed perpendicularly through the ribs, and the multiple layer sheet is stretched to separate each rib into a plurality of stems. The stems can be formed with a hooked shape or subsequently pressed against a heated surface to form a hook or capped stem.
The melt forming step can include simultaneously melt forming the first and second layers of material. The joining step can include: (a) joining together the first and second layers before any layer has cooled; (b) laminating the first and second layers; and/or (c) incorporating one or more reactive tie layers between the first and second layers. Melt forming can be accomplished by coextruding the first and second layers of material.
The inventive web can be stretched to surround an object or body to be fastened, secured or wrapped and relaxes to provide a constant tension that conforms to that body or object. It also exhibits substantially continuous fastening capability along its entire length. Instead of being formed from an elastic material having fastening means only at the ends of an elastic web, these continuous fastening constructions can have fastening means across or along the entire length and width of elastic web. Benefits realized from these constructions are at least two-fold: (1) such continuously-functional webs could be cut into any useful size and geometry and exhibit functionality, allowing for among other things a tape-like packaging; and (2) such continuously-functional webs would have more fastening capability per unit area.